1. Field of the Invention
The invention relates generally to an improved method for retreading the running surface of vehicle tires and more particularly to a novel method for applying a prevulcanized tread strip directly to a tire casing by cold vulcanization for the purpose of replacing such tread as may have been previously worn off in use or otherwise removed from the tire.
2. Description of the Prior Art
Heretofore, various methods have been employed for retreading vehicle tires. Commonly, worn tires are recapped by the warm vulcanization method, wherein an uncured thread cover of "camel-back" is applied to the buffed crown surface of the previously cured tire casing or carcass and the assembly is vulcanized at an elevated temperature in a suitable mold. A major disadvantage of this type of retread resides in the finished or vulcanized tread surface which is relatively microporous and will quickly wear off in use, thereby materially reducing the service-life of the retreaded tire. This is primarily due to the fact that the uncured "camel-back" cannot be subjected to an extremely high molding pressure while being vulcanized to the tire casing. Any deformation or distortion of the tire casing during the curing operation will tend to subsequently rupture or materially weaken the vulcanized bond between the cured "camel-back" and the crown surface of the tire after it is removed from the vulcanizing mold. In addition, the elevated vulcanizing temperature tends to weaken and deteriorate the previously cured tire casing.
More recently, attempts have been made to apply a prevulcanized tread strip to a previously cured tire casing by "cold" vulcanization. The prevulcanized tread strip is bonded directly to the tire casing by means of a bonding material without subjecting the tire casing to an elevated vulcanizing temperature which would tend to weaken and deteriorate the previously cured tire casing. In addition, since the tread strip is vulcanized before being applied to the tire casing, considerably increased vulcanization pressures may be employed which result in a retread surface having improved strength and density and which will tend to resist normal road abrasion. A retread having such a prevulcanized tread strip uniformly and securely bonded thereto will accordingly have a greatly increased service-life. In the past, efforts to bond a prevulcanized strip to a tire casing have not cured the tire to its normal inflated radius resulting in inferior tire mileage. Earlier methods involve slow loading of single tires into a chamber thereby allowing the chamber to cool down. Other methods do not allow a visual inspection of an inflated assembly outside of the curing station to determine if the envelope containing the assembled unit has no leaks and will sustain a vacuum. The failure of prior art methods to effect a satisfactory uniform bond between the prevulcanized tread strip and the tire casing has generally been due to two factors. First, deformation and shrinkage of the tire casing due to the application of pressure thereto during the bonding operation, and, second, the entrapment of air between the tread strip and the tire casing that is not forced out during the curing.